1. Field of the Invention
This invention relates to optical pickup (read/write head) for optical disc drives, and more particularly, to a curved-beam supporting structure for used on the objective-lens driving unit (actuator) of an optical pickup to support the focusing and tracking movements of the actuator.
2. Description of Related Art
Optical discs are a mass storage medium that can store a large amount of digital data thereon, which can be read by using optical disc drives. An optical disc drive is provided with an optical pickup (read/write head) for reading the data stored on an optical disc. During read operation, the optical pickup should be capable of focusing a laser beam precisely on the target track where the data to be read out are located. An objective lens is used for the focusing purpose. A driving unit (or called actuator) is used to move the objective lens in various directions during the focusing and tracking operations to bring the laser beam into focused and tracked condition. Defocusing and mistracking of the laser beam are usually caused by deviations and oscillations of the optical disc being read. The actuator should have the following features: (1) high sensitivity; (2) good dynamic characteristics, such as the capability to maintain stable operation in high-frequency regions; and (3) compact in size and low in manufacturing cost.
In the optical pickup, a supporting structure is used to support the actuator in such a manner that the actuator can freely move in both the focusing and tracking directions. A conventional type of supporting structure for the optical pickup actuator includes four parallel oriented straight beams to support the focusing and tracking movements of the optical pickup actuator, such as the one disclosed in the U.S. Pat. No. 4,842,392 "OBJECTIVE LENS DRIVING UNIT" to Nakamura. This patent discloses a parallel-beam supporting structure which is characterized in that the center of the driving force is coincident with the center of weight of the moving parts of the actuator. One drawback to the conventional parallel-beam supporting structure, however, is that it can cause the actuator to suffer from resonance that are caused by internal electromagnetic reaction forces. This drawback would cause the servo control for the focusing and tracking operations to be unstable.